EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN)
CERN-PH-EP/2012-025 2013/02/20
CMS-HIG-11-025
Search for the standard model Higgs boson in the decay
channel H
→
ZZ
→
4
`
in pp collisions at
√
s
=
7 TeV
The CMS Collaboration
∗Abstract
A search for a Higgs boson in the four-lepton decay channel H → ZZ, with each Z boson decaying to an electron or muon pair, is reported. The search covers Higgs boson mass hypotheses in the range 110 < mH < 600 GeV. The analysis uses data corresponding to an integrated luminosity of 4.7 fb−1recorded by the CMS detector in pp collisions at√s = 7 TeV from the LHC. Seventy-two events are observed with four-lepton invariant mass m4` > 100 GeV (with thirteen below 160 GeV), while 67.1±6.0
(9.5±1.3) events are expected from background. The four-lepton mass distribution is consistent with the expectation of standard model background production of ZZ pairs. Upper limits at 95% confidence level exclude the standard model Higgs boson in the ranges 134–158 GeV, 180–305 GeV, and 340–465 GeV. Small excesses of events are observed around masses of 119, 126, and 320 GeV, making the observed limits weaker than expected in the absence of a signal.
Submitted to Physical Review Letters
∗See Appendix A for the list of collaboration members
The standard model (SM) of electroweak interactions [1–3] relies on a scalar particle, the Higgs boson, associated with the field responsible for the spontaneous electroweak symmetry break-ing [4–9]. The existence of the Higgs boson has yet to be established experimentally, while its mass, mH, is not fixed by the theory. Direct searches for the SM Higgs boson at the LEP e+e− collider and the Tevatron pp collider have led, respectively, to a lower mass bound of mH > 114.4 GeV [10], and to an exclusion in the range 162–166 GeV [11], at 95% CL. Indirect constraints from precision measurements favour the mass range mH <158 GeV [12] at 95% CL. The inclusive Higgs boson production followed by the decay H → ZZ is expected to be one of the main discovery channels at the CERN proton-proton (pp) Large Hadron Collider (LHC) for a wide range of mHvalues. Using the H →ZZ and the H →WW decay channels, the AT-LAS collaboration have excluded at 95% CL the mass ranges 145–206 GeV, 214–224 GeV, and 340–450 GeV [13–15].
In this Letter, an inclusive search in the four-lepton decay channel, H→ZZ→ `+`−`0+`0−with
`,`0 = e or µ, abbreviated as H→4`, is presented. The analysis is designed for a Higgs boson in the mass range 110<mH <600 GeV. It uses pp data from the LHC collected at
√
s = 7 TeV by the Compact Muon Solenoid (CMS) experiment during 2010 and 2011. The data corresponds to an integrated luminosity of 4.7 fb−1. The search relies solely on the measurement of leptons, and the analysis achieves high lepton reconstruction, identification, and isolation efficiencies for a ZZ → 4` system composed of two pairs of same-flavour and opposite-charge isolated leptons, e+e−or µ+µ−, in the measurement range m4` >100 GeV. One or both of the Z bosons
can be off-shell. The background sources include an irreducible four-lepton contribution from direct ZZ production via qq annihilation and gg fusion. Reducible contributions arise from Zbb and tt where the final states contain two isolated leptons and two b jets producing secondary leptons. Additional background of instrumental nature arises from Z+jets events where jets are misidentified as leptons.
Particles produced in the pp collisions are detected in the pseudorapidity range|η| <5, where η= −ln tan(θ/2)and θ is the polar angle with respect to the direction of the proton beam. The
CMS detector comprises a superconducting solenoid, providing a uniform magnetic field of 3.8 T in the bore, equipped with silicon pixel and strip tracking systems (|η| <2.5) surrounded
by a lead tungstate crystal electromagnetic calorimeter (ECAL) and a brass-scintillator hadronic calorimeter (HCAL) (|η| < 3.0). A steel/quartz-fiber Cherenkov calorimeter extends the
cov-erage (|η| < 5). The steel return yoke outside the solenoid is instrumented with gas detectors
used to identify muons (|η| <2.4). A detailed description of the detector is given in Ref. [16].
Monte Carlo (MC) samples for the SM Higgs boson signal and for background processes are used to optimize the event selection and to evaluate the acceptance and systematic uncer-tainties. The Higgs boson signals from gluon-fusion (gg → H), and vector-boson fusion (qq → qqH), are generated with POWHEG [17] at next-to-leading-order (NLO) and a
dedi-cated generator from Ref. [18]. Additional samples of WH, ZH, and ttH events are generated
withPYTHIA[19]. Events at generator level are reweighted according to the total cross section
σ(pp → H), which contains contributions from gluon fusion up to
next-to-next-to-leading-order (NNLO) and next-next-to-leading-log taken from Refs. [20–29] and from the weak-boson fusion contribution computed at NNLO in Refs. [22, 30–34]. The total cross section is scaled by the branching fractionB(H → 4`)[22, 35–38]. Interference effects in the 4e and 4µ chan-nels are calculated with PROPHECY4F [22, 35, 36]. The SM background contribution from ZZ
production via qq is generated at NLO withPOWHEG, while other di-boson processes (WW,
WZ) are generated withPYTHIAwith cross sections rescaled to NLO predictions. The gg→ZZ contribution is generated with GG2ZZ [39]. The Zbb, Zcc, Zγ, and Z+light jets samples are generated with MADGRAPH[40] with cross sections rescaled to NNLO prediction for inclusive
Z production. The tt events are generated at NLO with POWHEG. The generation takes into account the internal initial state and final state radiation (FSR) effects which can lead to the presence of additional hard photons in an event. All events are processed through a detailed simulation of the CMS detector based on GEANT4 [41] and are reconstructed with the same
algorithms that are used for data.
Collision events are selected by the trigger system that requires the presence of a pair of elec-trons (a pair of muons) with transverse energy (transverse momenta) for the first and second lepton above 17 and 8 GeV respectively. The trigger efficiency within the acceptance of this analysis is greater than 99% for signal in the 4e and 4µ channels, and rises from about 97.5% at mH =120 GeV to above 99% at mH >140 GeV in the 2e2µ channel, within the acceptance of this analysis.
Electrons are reconstructed within the geometrical acceptance,|ηe| <2.5, and with peT>7 GeV,
by combining information from the ECAL and inner tracker [42, 43]. Electron identification selection requirements rely on electromagnetic shower-shape observables and on observables combining tracker and calorimetry information. The selection criteria depend on peT and|ηe|,
and on a categorization according to observables sensitive to the amount of bremsstrahlung emitted along the trajectory in the inner tracker. Muons are reconstructed [44] within|ηµ| <2.4
and pTµ>5 GeV, using information from both the inner tracker and the muon spectrometer. The inner track is required to be composed of more than 10 tracker-layer hits to ensure a precise measurement of the momentum. The efficiencies are measured in data, using a tag-and-probe technique [45] based on an inclusive sample of Z events. The measurements are performed in several ranges in p`T and|η|. The product of reconstruction and identification efficiencies for
electrons in the ECAL barrel (endcaps) vary from about 68% (62%) for 7 < peT < 10 GeV to 82% (74%) at peT ' 10 GeV, and reach 90% (89%) for peT ' 20 GeV. It drops to about 85% in the transition region, 1.44 < |η| < 1.57, between the ECAL barrel and endcaps. The muons
are reconstructed and identified with efficiencies above∼98%. Lepton candidates are defined with a loose constraint on their isolation, by requiring the sum of the transverse momenta of tracks i within a cone around the lepton`of∆R= p(η`−ηi)2+ (φ`−φi)2 < 0.3, where φ is
the azimuthal angle, to have∑ipiT,track/p`T < 0.7. The lepton isolation efficiency for identified leptons with this very loose definition of isolation is found to be greater than 99%.
We first require a Z candidate formed with a pair of lepton candidates satisfying 50 < m1,2 < 120 GeV, p`1
T >20 GeV, and p
`2
T > 10 GeV. The pT thresholds ensure that the leptons are on the high-efficiency plateau for the trigger. The lepton pair is required to be well isolated using a combination of the tracker, ECAL and HCAL information. The sum of the combined relative isolation Risofor the two leptons is required to satisfy R`1
iso+R
`2
iso<0.35, where for each lepton, Riso = (1/p`T) × ∑ipi T,track+∑jE j T,ECAL+∑kEkT,HCAL
, with sums running over the charged tracks i, and the ETfrom energy deposits in cells j and k of the ECAL and HCAL within a cone of radius∆R<0.3, respectively. The footprint of the lepton is removed from the isolation sum. The combined isolation efficiencies measured with data using the tag-and-probe technique are found to be> 99% for muons and between 94% to 99% for electrons. The isolation is made largely insensitive to the number of overlapping pp interactions by correcting for the average energy flow [46] per unit area measured as a function of the number of primary vertices. The ratio of the efficiencies measured with data and with simulated Z → ``events is found to be consistent with unity. The significance of the signed impact parameter of each lepton relative to the event vertex, SIP3D = σIPIP, where IP is the impact parameter in three dimensions and σIP the associated uncertainty, is required to satisfy|SIP3D| <4. The`+`−pair with reconstructed mass closest to the nominal Z boson mass is retained and denoted Z1. The Z1+X dataset thus
defined contains the samples used to estimate reducible and instrumental backgrounds, as well as the ZZ rates. In the next step, a subset of events is identified with at least a third lepton candidate. The Z1+ `events are used to measure misidentified lepton rates. A subset of events with at least a fourth lepton candidate of any flavour or charge is then identified. Together, the Z1+ ` and Z1+ ``0 samples provide ways to estimate the remaining reducible (Zbb, tt) and instrumental (Z+light jets) backgrounds. For the signal, we select a second lepton pair, denoted Z2, from the remaining same flavour `+`− combinations, by requiring mZ2 >
12 GeV, with the restriction m4` > 100 GeV. For the 4e and 4µ final states, at least three of
the four combinations of opposite-sign pairs must satisfy m`` > 12 GeV. If more than one Z2 candidate satisfies all criteria, the ambiguity is resolved by choosing the leptons of highest pT. The isolation and impact parameter are used to further suppress the remaining backgrounds. We require for any combination of two leptons i and j, irrespective of flavour or charge, that Riso,i+Riso,j<0.35 and also impose|SIP3D| <4 for each of the four leptons.
Finally, to select the four-lepton signal candidates, we require that the Z1and Z2masses satisfy mminZ1 <mZ1 <120 GeV and m
min Z2 < mZ2 <120 GeV, with(m min Z1 , m min Z2 ) = (50, 12)GeV defining
the baseline selection and (mminZ1 , mminZ2 ) = (60, 60)GeV defining the high-mass selection. The baseline selection is used to search for the Higgs boson, and the high-mass selection is used to measure the ZZ cross section.
The event yields are found to be in good agreement with the MC background expectation at each step of event selection. The ZZ and Z+X backgrounds dominate after the full event selection. The overall signal detection efficiency for the 4e (4µ, 2e2µ) channel is evaluated by MC and increases from ≈21% (59%, 35%) at mH = 120 GeV to ≈35% (71%, 50%) at mH = 140 GeV, reaching a plateau at≈51% (81%, 63%) at mH = 200 GeV, and then slowly rising to
≈60% (83%, 72%) at mH = 350 GeV. The relative mass resolution estimated from MC signal samples is about 2.1% (1.1%, 1.6%) for 4e (4µ, 2e2µ).
The small number of observed events precludes a precise direct evaluation of background by extrapolating from mass sidebands. Instead, we rely on MC to evaluate the number of events expected from the ZZ background. The cross section for ZZ production at NLO, through the dominant process of qq annihilation and through gg fusion, is calculated withMCFM[47–49]. The theoretical uncertainties are computed as a function of m4`, varying both the QCD
renor-malization and factorization scales and the parton distribution functions (PDF) set following the PDF4LHC recommendations [50–54]. The uncertainties for the QCD and PDF scales for each final state are on average 8%. The number of predicted ZZ→ 4`events and their uncer-tainties after the baseline selection are given in Table 1. As a consistency check, an evaluation is made based on a normalization to the measured inclusive single-Z production, a procedure discussed in Refs. [55, 56]. The measured rate of single Z bosons defined in this analysis is used to predict the total ZZ rate; making use of the ratio of the theoretical cross sections for ZZ and Z production, and the ratio of the reconstruction and selection efficiencies for the four-lepton and two-lepton final states. The results are in agreement with the ZZ rates reported in Table 1 within uncertainties.
To estimate the reducible (Zbb, tt) and instrumental (Z+light jets) backgrounds, a region well separated from the signal region is defined by relaxing and inverting some selection criteria and verifying that the event rates change according to MC expectation. The event rates measured in the background control region are then extrapolated to the signal region. The control region for Z+X, where X stands for bb, cc, gluon or light quark jets, is obtained by relaxing the isolation and identification criteria for two additional reconstructed lepton objects (a measured track for muons, or a combination of a track and a cluster of ECAL energy deposits for electrons)
indi-cated as `reco`reco. The additional pair of leptons must have like sign charge (to avoid signal contamination) and same flavour (e±e±, µ±µ±), a reconstructed invariant mass mZ2 either
satis-fying the baseline selection or the high-mass selection, and m4`>100 GeV. A sample Z1+ `reco, with at least one reconstructed lepton object, is also defined for the measurement of the lepton misidentification probability, the probability for a reconstructed object to pass the isolation and identification requirements. The contamination from WZ in this set of events is suppressed by requiring that the imbalance of the measured energy deposition in the transverse plane is be-low 25 GeV. From the Z+ `reco`recosample the expected number of Z+X background events in the signal region is obtained by taking into account the lepton misidentification probability for each of the two additional leptons. The number of background events expected in the signal region, normalized to the integrated luminosity, and the associated systematic uncertainties, are given in Table 1 for the baseline selection in the range 100<m4` < 600 GeV. The reducible
and instrumental background is found to be dominated by Z+light jets. A small residual contamination of Zbb remains at low mass while for the high-mass selection these reducible backgrounds are an order of magnitude smaller and therefore can be neglected. This was ver-ified by performing a measurement of Zbb and tt rates in a dedicated four-lepton background control region, defined by requiring a Z1 and two additional leptons satisfying an inverted SIP3D requirement, namely |SIP3D| > 5, and with relaxed isolation, charge, and flavour re-quirements. This ensures a negligible Z+light jets contribution in the four-lepton background control region, while the signal and the ZZ background are absent. To extract background rates, the reconstructed Z1mass for the sum of the Z1+2e, Z1+2µ, and Z1+eµ final states is fit with a Breit-Wigner function convoluted with a Crystal Ball function [57] for the Z1peak from Zbb and Chebychev polynomials for the description of the tt continuum. The extrapolation to the signal region relies on knowledge of, and the distinct features of, the SIP3Ddistributions for the Z2 leptons of the tt and Zbb backgrounds. The result is found to be compatible with the MC expectation in the signal region within the systematic uncertainty of 20%.
Systematic uncertainties are evaluated from data for trigger efficiency (1.5%), lepton recon-struction and identification (2 – 3%), and isolation efficiencies (2%). Systematic uncertainties on energy-momentum calibration (0.5%), and energy resolution are accounted for by their ef-fect on the reconstructed mass distributions. The efef-fect of the energy resolution uncertainties is taken into account by introducing a 30% uncertainty on the width of the signal mass peak. Additional systematic uncertainties arise from limited statistics in the reducible background control regions. All reducible and instrumental background sources are derived from control regions, and the comparison of data with the background expectation in the signal region is independent of the uncertainty on the LHC integrated luminosity of the data sample. This uncertainty (4.5%) [58] enters the evaluation of the ZZ background and in the calculation of the cross section limit through the normalization of the signal. Systematic uncertainties on the Higgs boson cross section (17 – 20%) and branching fraction (2%) are taken from Ref. [22]. Recent studies [22, 59, 60] show that current Monte Carlo simulations do not describe the ex-pected Higgs boson mass line shape above≈300 GeV. These effects are estimated to amount to an additional uncertainty on the theoretical cross section, and hence on the limits, of about 4% at mH=300 GeV and 10 – 30% for mHof 400–600 GeV.
The number of candidates observed, as well as the estimated background in the signal region, are reported in Table 1 for the baseline selection. The reconstructed four-lepton invariant mass distribution for the combined 4e, 4µ, and 2e2µ channels with the baseline selection is shown in Fig. 1a and compared to expectations from the backgrounds. The shape of the mass distribution below mH = 180 GeV reflects the shape of the dominant qq annihilation process [61]. The low mass range is shown in Fig. 1b together with the mass of each candidate and its uncertainty.
m
4[GeV]
Eve n ts/ 1 0 G e V]
2[GeV/c
4lM
100 200 300 400 500 600 2Events/10 GeV/c
0 2 4 6 8 10 12 14 16 18 DATA Z+X ZZ 2 =350 GeV/c H m 2 =200 GeV/c H m 2 =140 GeV/c H m CMS Preliminary 2011CMS s = 7 TeV L = 4.71 fbL = 4.7 fb-1-1 10 100 0 ] 2 [GeV/c 4l M 100 200 300 400 500 600 2 Events/10 GeV/c 0 2 4 6 8 10 12 14 16 18 ] 2 [GeV/c 4l M 100 200 300 400 500 600 2 Events/10 GeV/c 0 2 4 6 8 10 12 14 16 18 DATA Z+X ZZ 2 =140 GeV/c H m 2 =200 GeV/c H m 2 =350 GeV/c H m CMS Preliminary 2011s = 7 TeV L = 4.71 fb-1 sback ] 2 [GeV/c 4l M 100 110 120 130 140 150 160 2 Events/2 GeV/c 0 1 2 3 4 5 6 DATA Z+X ZZ 2 =140 GeV/c H m 2 =120 GeV/c H m CMS Preliminary 2011 s = 7 TeV L = 4.73 fb-1 ] 2 [GeV/c 4l M 100 200 300 400 500 600 2 Events/10 GeV/c 0 2 4 6 8 10 12 14 16 18 DATA Z+X ZZ 2 =350 GeV/c H m 2 =200 GeV/c H m 2 =140 GeV/c H m CMS Preliminary 2011 s = 7 TeV L = 4.71 fb-1 Data Z+X ZZ mH = 140 GeV mH = 200 GeV mH = 350 GeV ] 2 [GeV/c 4l M 100 200 300 400 500 600 2 Events/10 GeV/c 0 2 4 6 8 10 12 14 16 18 ] 2 [GeV/c 4l M 100 200 300 400 500 600 2 Events/10 GeV/c 0 2 4 6 8 10 12 14 16 18 DATA Z+X ZZ 2 =140 GeV/c H m 2 =200 GeV/c H m 2 =350 GeV/c H m CMS Preliminary 2011 -1 = 7 TeV L = 4.71 fb s sback a) 12 14 16 18 2 4 6 8 200 300 400 500 600]
2[GeV/c
4lM
100 200 300 400 500 600 2Events/10 GeV/c
0 2 4 6 8 10 12 14 16 18 DATA Z+X ZZ 2 =350 GeV/c H m 2 =200 GeV/c H m 2 =140 GeV/c H m CMS Preliminary 2011 s = 7 TeV L = 4.71 fb-1 ] 2 [GeV/c 4l M 100 110 120 130 140 150 160 2 Events/2 GeV/c 0 1 2 3 4 5 ] 2 [GeV/c 4l M 100 110 120 130 140 150 160 2 Events/2 GeV/c 0 1 2 3 4 5 DATA Z+X ZZ=140 GeV/c2 H m=120 GeV/c2 H m CMS Preliminary 2011s = 7 TeV L = 4.71 fb-1 sback Eve n ts/ 2 G e Vm
4[GeV]
0 2 100 110 120 130 140 150 160 0.99750.998 0.99850.999 0.99951 1.00051.001 100 110 120 130 140 150 160 0.99750.998 0.99850.999 0.99951 1.00051.001 100 110 120 130 140 150 160 1 3 4 5 L EP e xcl u d e d (9 5 % C L ) b) ] 2 [GeV/c 4l M 100 110 120 130 140 150 160 2 Events/2 GeV/c 0 1 2 3 4 5 6 DATA Z+X ZZ 2 =140 GeV/c H m 2 =120 GeV/c H m CMS Preliminary 2011 -1 = 7 TeV L = 4.73 fb s Z+X ZZ mH = 120 GeV mH = 140 GeV ] 2 [GeV/c 4l M 100 200 300 400 500 600 2 Events/10 GeV/c 0 2 4 6 8 10 12 14 16 18 ] 2 [GeV/c 4l M 100 200 300 400 500 600 2 Events/10 GeV/c 0 2 4 6 8 10 12 14 16 18 DATA Z+X ZZ 2 =140 GeV/c H m 2 =200 GeV/c H m 2 =350 GeV/c H m CMS Preliminary 2011s = 7 TeV L = 4.71 fb-1 sback ] 2 [GeV/c 4l M 100 200 300 400 500 600 2 Events/10 GeV/c 0 2 4 6 8 10 12 14 16 18 ] 2 [GeV/c 4l M 100 200 300 400 500 600 2 Events/10 GeV/c 0 2 4 6 8 10 12 14 16 18 DATA Z+X ZZ 2 =140 GeV/c H m 2 =200 GeV/c H m 2 =350 GeV/c H m CMS Preliminary 2011s = 7 TeV L = 4.71 fb-1 sback Data[ 4e, 4μ, 2e2μ ] CMS L = 4.7 fb-1Figure 1: a) Distribution of the four-lepton reconstructed mass for the sum of the 4e, 4µ, and 2e2µ channels. b) Expansion of the low mass range with existing exclusion limits at 95% CL; also shown are the central values and individual candidate mass measurement uncertainties. Points represent the data, shaded histograms represent the background and unshaded his-togram the signal expectations.
The reducible and instrumental background rates are small. These rates have been obtained from data and the corresponding m4`distributions are obtained from MC samples.
The measured distribution is compatible with the expectation from SM direct production of ZZ pairs. We observe 72 candidates, 12 in 4e, 23 in 4µ, and 37 in 2e2µ, while 67.1±6.0 events are expected from standard model background processes. No hard photon (pγT > 5 GeV) was found, outside the isolation veto cone that surrounds each lepton, that could be unambiguously identified as FSR. Thirteen candidates are observed within 100< m4`<160 GeV while 9.5±1.3
background events are expected. We observe 53 candidates for the high-mass selection com-pared to an expectation of 51.3±4.6 events from background. This high-mass event selection is used to provide a measurement of the total cross section σ(pp→ZZ+X) × B(ZZ→4`) =
28.1+−4.64.0(stat.) ±1.2(syst.) ±1.3(lumi.)fb. The measurement agrees with the SM prediction at NLO [47] of 27.9±1.9 fb. The local p-values, representing the significance of local excesses relative to the standard model expectation, are shown as a function of mHin Fig. 2a, obtained either taking into account or not the individual candidate mass measurement uncertainties,
Table 1: The number of candidates observed, compared to background and signal rates for each final state for 100 < m4` < 600 GeV for the baseline selection. For the Z+X background,
the estimations are based on data
Channel 4e 4µ 2e2µ ZZ background 12.27±1.16 19.11±1.75 30.25±2.78 Z+X 1.67±0.55 1.13±0.55 2.71±0.96 All background 13.94±1.28 20.24±1.83 32.96±2.94 mH=120 GeV 0.25 0.62 0.68 mH=140 GeV 1.32 2.48 3.37 mH=350 GeV 1.95 2.61 4.64 Observed 12 23 37
for the combination of the three channels. Excesses are observed for masses near 119 GeV and 320 GeV. The small ≈2σ excess near 320 GeV includes three events with p4T` > 50 GeV. The most significant excess near 119 GeV corresponds to about 2.5σ significance. The significance is less than 1.0σ (about 1.6σ) when the look-elsewhere effect [62] is accounted for over the full mass range (for the low-mass range 100 < m4` < 160 GeV). The local significances change
only slightly when including candidate mass uncertainties, instead of using the average mass resolution, e.g. rising to 2.7σ around 119 GeV and reaching 1.5σ around 126 GeV.
] 2 [GeV/c 4l M 100 200 300 400 500 600 2 Events/10 GeV/c 0 2 4 6 8 10 12 14 16 18 DATA Z+X ZZ 2 =350 GeV/c H m 2 =200 GeV/c H m 2 =140 GeV/c H m CMS Preliminary 2011 s = 7 TeV L = 4.71 fb-1 ] 2 [GeV/c H Higgs mass, m 200 300 400 500 600 p-value -4 10 -3 10 -2 10 -1 10 1 -1 = ~4.7 fb int =7 TeV L s CMS Private
4l ( without event-by-event mass resolution )
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H A ZZ A 4l ( with event-by-event mass resolution ) H ] 2 [GeV/c H Higgs mass, m 110 115 120 125 130 135 140 145 150 155 160 p-value -3 10 -2 10 -1 10 1 -1 = ~4.7 fb int =7 TeV L s CMS Private
4l ( without event-by-event mass resolution )
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H A ZZ A 4l ( with event-by-event mass resolution )
H 600 lo ca l p -va lu e 10-3 10-2 10-1 10-4 1 1σ 2σ 3σ mH [GeV] 1σ 2σ 3σ mH [GeV] Expected ± 1σ CMS L = 4.7 fb-1 120 140 w/o m4 uncertainties with m4 uncertainties lo ca l p -va lu e 1 10-2 a) 110 200 300 400 500 ] 2 [GeV/c H M 200 300 400 500 SM 4l) A ZZ A (H m/ 95% CL 4l) A ZZ A (H m 1 10 ] 2 [GeV/c H M 110 120 130 140 150 SM 4l) A ZZ A (H m/ 95% CL 4l) A ZZ A (H m 1 10 ] 2 [GeV/c H M 120 140 160 180 4l) A ZZ A (H m/ 95% CL 4l) A ZZ A (H m -1 10 1 10 ] 2 [GeV/c H M 120 140 160 180 SM 4l) A ZZ A (H m/ 95% CL 4l) A ZZ A (H m -1 10 1 10 ] 2 [GeV/c H M 120 140 160 180 SM 4l) A ZZ A (H m/ 95% CL 4l) A ZZ A (H m -1 10 1 10 9 5 % C L l imi t o n ] 2 [GeV/c 4l M 100 200 300 400 500 600 2 Events/10 GeV/c 0 2 4 6 8 10 12 14 16 18 DATA Z+X ZZ 2 =350 GeV/c H m 2 =200 GeV/c H m 2 =140 GeV/c H m CMS Preliminary 2011 s = 7 TeV L = 4.71 fb-1 ] 2 [GeV/c H Higgs mass, m 200 300 400 500 600 p-value -4 10 -3 10 -2 10 -1 10 1 -1 = ~4.7 fb int =7 TeV L s CMS Private
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H A ZZ A 4l ( with event-by-event mass resolution ) H 10 1 CMS L = 4.7 fb-1 b) Expected ± 1σ Expected ± 2σ Observed ] 2 [GeV/c H M 120 140 160 180 SM 4l) A ZZ A (H m/ 95% CL 4l) A ZZ A (H m -1 10 1 10 ] 2 [GeV/c H M 120 140 160 180 SM 4l) A ZZ A (H m/ 95% CL 4l) A ZZ A (H m -1 10 1 10 ] 2 [GeV/c H M 120 140 160 180 SM 4l) A ZZ A (H m/ 95% CL 4l) A ZZ A (H m -1 10 1 10 600 110 200 300 400 500 mH [GeV] 1 140 120 m H [GeV] 10
Figure 2: a) The significance of the local excesses with respect to the standard model expectation as a function of the Higgs boson mass, without (blue) or with (red) individual candidate mass measurement uncertainties. b) The observed and the median expected upper limits at 95% CL on σ(pp→H+X) × B(ZZ→4`), normalized to the standard model cross section values σSM, for a Higgs boson in the mass range 110–600 GeV, using the CLsapproach. The insets expand the low mass range.
In absence of a significant clustering of candidates at any given mass, we derive exclusion lim-its. The exclusion limits for a SM-like Higgs boson are computed for a large number of mass points in the mass range 110–600 GeV, using the predicted signal and background mass distri-bution shapes. The choice of the step size in the scan between Higgs mass hypotheses is driven by either detector resolution, or the natural width of the Higgs boson. The signal mass distri-butions shapes are determined using simulated samples for 27 values of mHcovering the full mass range. The shapes are fit using a function obtained from a convolution of a Breit-Wigner probability density function to describe the theoretical resonance line shape and a Crystal Ball function to account for the detector effects. The parameters of the Crystal Ball function are interpolated for the mH points where there is no simulated sample available. The shapes of the background mass distributions are determined by fits to the simulated sample of events, while the normalization is taken from estimates of overall event yields as described above. For each mass hypothesis, we perform an unbinned likelihood fit using the statistical approach discussed in Ref. [63]. We account for systematic uncertainties in the form of nuisance parame-ters with a log-normal probability density function. The observed and median expected upper limits on σ(pp → H+X) × B(H→ ZZ) × B(ZZ→ 4`)at 95% CL are shown in Fig. 2b. The limits are calculated relative to the expected SM Higgs boson cross section values σSM, using the modified frequentist method CLs [64, 65]. The bands represent the 1σ and 2σ probabil-ity intervals around the expected limit. These upper limits exclude the standard model Higgs boson at 95% CL in the mH ranges 134–158 GeV, 180–305 GeV and 340–465 GeV. The limits re-flect the dependence of the branching ratioB(H → ZZ)on mH. The worsening of the limits at high mass arises from the decreasing cross section for the H → 4`signal. By virtue of the
excellent mass resolution and low background, the structure in the measured limits follows the fluctuations of the number of observed events.
In summary, a search for the standard model Higgs boson has been presented in the four-lepton decay modes. Upper limits at 95% confidence level exclude the Higgs boson mass ranges 134–158 GeV, 180–305 GeV, and 340–465 GeV. A major fraction of the explored mass range is thus excluded at 95% CL and the exclusion limits extend beyond the sensitivity of previous collider experiments. Excesses of events are observed at the low end of the explored mass range, around masses of 119 and 126 GeV, and at high mass around 320 GeV. These excesses, although not statistically significant, make the observed limits weaker than expected in the absence of a signal. At low mass, only the region 114.4 < mH < 134 GeV remains consistent with the expectation for the standard model Higgs boson production.
We wish to congratulate our colleagues in the CERN accelerator departments for the excellent performance of the LHC machine. We thank the technical and administrative staff at CERN and other CMS institutes, and acknowledge support from: FMSR (Austria); FNRS and FWO (Bel-gium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MoST, and NSFC (China); COLCIENCIAS (Colombia); MSES (Croatia); RPF (Cyprus); Academy of Sci-ences and NICPB (Estonia); Academy of Finland, MEC, and HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NKTH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); NRF and WCU (Korea); LAS (Lithua-nia); CINVESTAV, CONACYT, SEP, and UASLP-FAI (Mexico); MSI (New Zealand); PAEC (Pak-istan); MSHE and NSC (Poland); FCT (Portugal); JINR (Armenia, Belarus, Georgia, Ukraine, Uzbekistan); MON, RosAtom, RAS and RFBR (Russia); MSTD (Serbia); MICINN and CPAN (Spain); Swiss Funding Agencies (Switzerland); NSC (Taipei); TUBITAK and TAEK (Turkey); STFC (United Kingdom); DOE and NSF (USA).
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A
The CMS Collaboration
Yerevan Physics Institute, Yerevan, Armenia
S. Chatrchyan, V. Khachatryan, A.M. Sirunyan, A. Tumasyan
Institut f ¨ur Hochenergiephysik der OeAW, Wien, Austria
W. Adam, T. Bergauer, M. Dragicevic, J. Er ¨o, C. Fabjan, M. Friedl, R. Fr ¨uhwirth, V.M. Ghete, J. Hammer1, M. Hoch, N. H ¨ormann, J. Hrubec, M. Jeitler, W. Kiesenhofer, M. Krammer, D. Liko, I. Mikulec, M. Pernicka†, B. Rahbaran, C. Rohringer, H. Rohringer, R. Sch ¨ofbeck, J. Strauss, A. Taurok, F. Teischinger, P. Wagner, W. Waltenberger, G. Walzel, E. Widl, C.-E. Wulz
National Centre for Particle and High Energy Physics, Minsk, Belarus
V. Mossolov, N. Shumeiko, J. Suarez Gonzalez
Universiteit Antwerpen, Antwerpen, Belgium
S. Bansal, L. Benucci, T. Cornelis, E.A. De Wolf, X. Janssen, S. Luyckx, T. Maes, L. Mucibello, S. Ochesanu, B. Roland, R. Rougny, M. Selvaggi, H. Van Haevermaet, P. Van Mechelen, N. Van Remortel, A. Van Spilbeeck
Vrije Universiteit Brussel, Brussel, Belgium
F. Blekman, S. Blyweert, J. D’Hondt, R. Gonzalez Suarez, A. Kalogeropoulos, M. Maes, A. Olbrechts, W. Van Doninck, P. Van Mulders, G.P. Van Onsem, I. Villella
Universit´e Libre de Bruxelles, Bruxelles, Belgium
O. Charaf, B. Clerbaux, G. De Lentdecker, V. Dero, A.P.R. Gay, G.H. Hammad, T. Hreus, A. L´eonard, P.E. Marage, L. Thomas, C. Vander Velde, P. Vanlaer, J. Wickens
Ghent University, Ghent, Belgium
V. Adler, K. Beernaert, A. Cimmino, S. Costantini, G. Garcia, M. Grunewald, B. Klein, J. Lellouch, A. Marinov, J. Mccartin, A.A. Ocampo Rios, D. Ryckbosch, N. Strobbe, F. Thyssen, M. Tytgat, L. Vanelderen, P. Verwilligen, S. Walsh, E. Yazgan, N. Zaganidis
Universit´e Catholique de Louvain, Louvain-la-Neuve, Belgium
S. Basegmez, G. Bruno, L. Ceard, J. De Favereau De Jeneret, C. Delaere, T. du Pree, D. Favart, L. Forthomme, A. Giammanco2, G. Gr´egoire, J. Hollar, V. Lemaitre, J. Liao, O. Militaru, C. Nuttens, D. Pagano, A. Pin, K. Piotrzkowski, N. Schul
Universit´e de Mons, Mons, Belgium
N. Beliy, T. Caebergs, E. Daubie
Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro, Brazil
G.A. Alves, M. Correa Martins Junior, D. De Jesus Damiao, T. Martins, M.E. Pol, M.H.G. Souza
Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil
W.L. Ald´a J ´unior, W. Carvalho, A. Cust ´odio, E.M. Da Costa, C. De Oliveira Martins, S. Fonseca De Souza, D. Matos Figueiredo, L. Mundim, H. Nogima, V. Oguri, W.L. Prado Da Silva, A. Santoro, S.M. Silva Do Amaral, L. Soares Jorge, A. Sznajder
Instituto de Fisica Teorica, Universidade Estadual Paulista, Sao Paulo, Brazil
T.S. Anjos3, C.A. Bernardes3, F.A. Dias4, T.R. Fernandez Perez Tomei, E. M. Gregores3, C. Lagana, F. Marinho, P.G. Mercadante3, S.F. Novaes, Sandra S. Padula
Institute for Nuclear Research and Nuclear Energy, Sofia, Bulgaria
V. Genchev1, P. Iaydjiev1, S. Piperov, M. Rodozov, S. Stoykova, G. Sultanov, V. Tcholakov, R. Trayanov, M. Vutova
University of Sofia, Sofia, Bulgaria
A. Dimitrov, R. Hadjiiska, A. Karadzhinova, V. Kozhuharov, L. Litov, B. Pavlov, P. Petkov
Institute of High Energy Physics, Beijing, China
J.G. Bian, G.M. Chen, H.S. Chen, C.H. Jiang, D. Liang, S. Liang, X. Meng, J. Tao, J. Wang, J. Wang, X. Wang, Z. Wang, H. Xiao, M. Xu, J. Zang, Z. Zhang
State Key Lab. of Nucl. Phys. and Tech., Peking University, Beijing, China
C. Asawatangtrakuldee, Y. Ban, S. Guo, Y. Guo, W. Li, S. Liu, Y. Mao, S.J. Qian, H. Teng, S. Wang, B. Zhu, W. Zou
Universidad de Los Andes, Bogota, Colombia
A. Cabrera, B. Gomez Moreno, A.F. Osorio Oliveros, J.C. Sanabria
Technical University of Split, Split, Croatia
N. Godinovic, D. Lelas, R. Plestina5, D. Polic, I. Puljak1
University of Split, Split, Croatia
Z. Antunovic, M. Dzelalija, M. Kovac
Institute Rudjer Boskovic, Zagreb, Croatia
V. Brigljevic, S. Duric, K. Kadija, J. Luetic, S. Morovic
University of Cyprus, Nicosia, Cyprus
A. Attikis, M. Galanti, J. Mousa, C. Nicolaou, F. Ptochos, P.A. Razis
Charles University, Prague, Czech Republic
M. Finger, M. Finger Jr.
Academy of Scientific Research and Technology of the Arab Republic of Egypt, Egyptian Network of High Energy Physics, Cairo, Egypt
Y. Assran6, A. Ellithi Kamel7, S. Khalil8, M.A. Mahmoud9, A. Radi10
National Institute of Chemical Physics and Biophysics, Tallinn, Estonia
A. Hektor, M. Kadastik, M. M ¨untel, M. Raidal, L. Rebane, A. Tiko
Department of Physics, University of Helsinki, Helsinki, Finland
V. Azzolini, P. Eerola, G. Fedi, M. Voutilainen
Helsinki Institute of Physics, Helsinki, Finland
S. Czellar, J. H¨ark ¨onen, A. Heikkinen, V. Karim¨aki, R. Kinnunen, M.J. Kortelainen, T. Lamp´en, K. Lassila-Perini, S. Lehti, T. Lind´en, P. Luukka, T. M¨aenp¨a¨a, T. Peltola, E. Tuominen, J. Tuominiemi, E. Tuovinen, D. Ungaro, L. Wendland
Lappeenranta University of Technology, Lappeenranta, Finland
K. Banzuzi, A. Korpela, T. Tuuva
Laboratoire d’Annecy-le-Vieux de Physique des Particules, IN2P3-CNRS, Annecy-le-Vieux, France
D. Sillou
DSM/IRFU, CEA/Saclay, Gif-sur-Yvette, France
M. Besancon, S. Choudhury, M. Dejardin, D. Denegri, B. Fabbro, J.L. Faure, F. Ferri, S. Ganjour, A. Givernaud, P. Gras, G. Hamel de Monchenault, P. Jarry, E. Locci, J. Malcles, L. Millischer, J. Rander, A. Rosowsky, I. Shreyber, M. Titov
Laboratoire Leprince-Ringuet, Ecole Polytechnique, IN2P3-CNRS, Palaiseau, France
S. Baffioni, F. Beaudette, L. Benhabib, L. Bianchini, M. Bluj11, C. Broutin, P. Busson, C. Charlot, N. Daci, T. Dahms, L. Dobrzynski, S. Elgammal, R. Granier de Cassagnac, M. Haguenauer, P. Min´e, C. Mironov, C. Ochando, P. Paganini, D. Sabes, R. Salerno, Y. Sirois, C. Thiebaux, C. Veelken, A. Zabi
Institut Pluridisciplinaire Hubert Curien, Universit´e de Strasbourg, Universit´e de Haute Alsace Mulhouse, CNRS/IN2P3, Strasbourg, France
J.-L. Agram12, J. Andrea, D. Bloch, D. Bodin, J.-M. Brom, M. Cardaci, E.C. Chabert, C. Collard, E. Conte12, F. Drouhin12, C. Ferro, J.-C. Fontaine12, D. Gel´e, U. Goerlach, P. Juillot, M. Karim12, A.-C. Le Bihan, P. Van Hove
Centre de Calcul de l’Institut National de Physique Nucleaire et de Physique des Particules (IN2P3), Villeurbanne, France
F. Fassi, D. Mercier
Universit´e de Lyon, Universit´e Claude Bernard Lyon 1, CNRS-IN2P3, Institut de Physique Nucl´eaire de Lyon, Villeurbanne, France
C. Baty, S. Beauceron, N. Beaupere, M. Bedjidian, O. Bondu, G. Boudoul, D. Boumediene, H. Brun, J. Chasserat, R. Chierici1, D. Contardo, P. Depasse, H. El Mamouni, A. Falkiewicz, J. Fay, S. Gascon, M. Gouzevitch, B. Ille, T. Kurca, T. Le Grand, M. Lethuillier, L. Mirabito, S. Perries, V. Sordini, S. Tosi, Y. Tschudi, P. Verdier, S. Viret
Institute of High Energy Physics and Informatization, Tbilisi State University, Tbilisi, Georgia
D. Lomidze
RWTH Aachen University, I. Physikalisches Institut, Aachen, Germany
G. Anagnostou, S. Beranek, M. Edelhoff, L. Feld, N. Heracleous, O. Hindrichs, R. Jussen, K. Klein, J. Merz, A. Ostapchuk, A. Perieanu, F. Raupach, J. Sammet, S. Schael, D. Sprenger, H. Weber, B. Wittmer, V. Zhukov13
RWTH Aachen University, III. Physikalisches Institut A, Aachen, Germany
M. Ata, J. Caudron, E. Dietz-Laursonn, M. Erdmann, A. G ¨uth, T. Hebbeker, C. Heidemann, K. Hoepfner, T. Klimkovich, D. Klingebiel, P. Kreuzer, D. Lanske†, J. Lingemann, C. Magass, M. Merschmeyer, A. Meyer, M. Olschewski, P. Papacz, H. Pieta, H. Reithler, S.A. Schmitz, L. Sonnenschein, J. Steggemann, D. Teyssier, M. Weber
RWTH Aachen University, III. Physikalisches Institut B, Aachen, Germany
M. Bontenackels, V. Cherepanov, M. Davids, G. Fl ¨ugge, H. Geenen, M. Geisler, W. Haj Ahmad, F. Hoehle, B. Kargoll, T. Kress, Y. Kuessel, A. Linn, A. Nowack, L. Perchalla, O. Pooth, J. Rennefeld, P. Sauerland, A. Stahl, M.H. Zoeller
Deutsches Elektronen-Synchrotron, Hamburg, Germany
M. Aldaya Martin, W. Behrenhoff, U. Behrens, M. Bergholz14, A. Bethani, K. Borras, A. Burgmeier, A. Cakir, L. Calligaris, A. Campbell, E. Castro, D. Dammann, G. Eckerlin, D. Eckstein, A. Flossdorf, G. Flucke, A. Geiser, J. Hauk, H. Jung1, M. Kasemann, P. Katsas, C. Kleinwort, H. Kluge, A. Knutsson, M. Kr¨amer, D. Kr ¨ucker, E. Kuznetsova, W. Lange, W. Lohmann14, B. Lutz, R. Mankel, I. Marfin, M. Marienfeld, I.-A. Melzer-Pellmann, A.B. Meyer, J. Mnich, A. Mussgiller, S. Naumann-Emme, J. Olzem, A. Petrukhin, D. Pitzl, A. Raspereza, P.M. Ribeiro Cipriano, M. Rosin, J. Salfeld-Nebgen, R. Schmidt14, T. Schoerner-Sadenius, N. Sen, A. Spiridonov, M. Stein, J. Tomaszewska, R. Walsh, C. Wissing
University of Hamburg, Hamburg, Germany
C. Autermann, V. Blobel, S. Bobrovskyi, J. Draeger, H. Enderle, J. Erfle, U. Gebbert, M. G ¨orner, T. Hermanns, R.S. H ¨oing, K. Kaschube, G. Kaussen, H. Kirschenmann, R. Klanner, J. Lange, B. Mura, F. Nowak, N. Pietsch, C. Sander, H. Schettler, P. Schleper, E. Schlieckau, A. Schmidt, M. Schr ¨oder, T. Schum, H. Stadie, G. Steinbr ¨uck, J. Thomsen
Institut f ¨ur Experimentelle Kernphysik, Karlsruhe, Germany
C. Barth, J. Berger, T. Chwalek, W. De Boer, A. Dierlamm, G. Dirkes, M. Feindt, J. Gruschke, M. Guthoff1, C. Hackstein, F. Hartmann, M. Heinrich, H. Held, K.H. Hoffmann, S. Honc, I. Katkov13, J.R. Komaragiri, T. Kuhr, D. Martschei, S. Mueller, Th. M ¨uller, M. Niegel, A. N ¨urnberg, O. Oberst, A. Oehler, J. Ott, T. Peiffer, G. Quast, K. Rabbertz, F. Ratnikov, N. Ratnikova, M. Renz, S. R ¨ocker, C. Saout, A. Scheurer, P. Schieferdecker, F.-P. Schilling, M. Schmanau, G. Schott, H.J. Simonis, F.M. Stober, D. Troendle, J. Wagner-Kuhr, T. Weiler, M. Zeise, E.B. Ziebarth
Institute of Nuclear Physics ”Demokritos”, Aghia Paraskevi, Greece
G. Daskalakis, T. Geralis, S. Kesisoglou, A. Kyriakis, D. Loukas, I. Manolakos, A. Markou, C. Markou, C. Mavrommatis, E. Ntomari
University of Athens, Athens, Greece
L. Gouskos, T.J. Mertzimekis, A. Panagiotou, N. Saoulidou, E. Stiliaris
University of Io´annina, Io´annina, Greece
I. Evangelou, C. Foudas1, P. Kokkas, N. Manthos, I. Papadopoulos, V. Patras, F.A. Triantis
KFKI Research Institute for Particle and Nuclear Physics, Budapest, Hungary
A. Aranyi, G. Bencze, L. Boldizsar, C. Hajdu1, P. Hidas, D. Horvath15, A. Kapusi, K. Krajczar16, F. Sikler1, V. Veszpremi, G. Vesztergombi16
Institute of Nuclear Research ATOMKI, Debrecen, Hungary
N. Beni, J. Molnar, J. Palinkas, Z. Szillasi
University of Debrecen, Debrecen, Hungary
J. Karancsi, P. Raics, Z.L. Trocsanyi, B. Ujvari
Panjab University, Chandigarh, India
S.B. Beri, V. Bhatnagar, N. Dhingra, R. Gupta, M. Jindal, M. Kaur, J.M. Kohli, M.Z. Mehta, N. Nishu, L.K. Saini, A. Sharma, A.P. Singh, J. Singh, S.P. Singh
University of Delhi, Delhi, India
S. Ahuja, B.C. Choudhary, A. Kumar, A. Kumar, S. Malhotra, M. Naimuddin, K. Ranjan, V. Sharma, R.K. Shivpuri
Saha Institute of Nuclear Physics, Kolkata, India
S. Banerjee, S. Bhattacharya, S. Dutta, B. Gomber, S. Jain, S. Jain, R. Khurana, S. Sarkar
Bhabha Atomic Research Centre, Mumbai, India
R.K. Choudhury, D. Dutta, S. Kailas, V. Kumar, A.K. Mohanty1, L.M. Pant, P. Shukla
Tata Institute of Fundamental Research - EHEP, Mumbai, India
T. Aziz, S. Ganguly, M. Guchait17, A. Gurtu18, M. Maity19, G. Majumder, K. Mazumdar, G.B. Mohanty, B. Parida, A. Saha, K. Sudhakar, N. Wickramage
Tata Institute of Fundamental Research - HECR, Mumbai, India
Institute for Research in Fundamental Sciences (IPM), Tehran, Iran
H. Arfaei, H. Bakhshiansohi20, S.M. Etesami21, A. Fahim20, M. Hashemi, H. Hesari, A. Jafari20, M. Khakzad, A. Mohammadi22, M. Mohammadi Najafabadi, S. Paktinat Mehdiabadi, B. Safarzadeh23, M. Zeinali21
INFN Sezione di Baria, Universit`a di Barib, Politecnico di Baric, Bari, Italy
M. Abbresciaa,b, L. Barbonea,b, C. Calabriaa,b, S.S. Chhibraa,b, A. Colaleoa, D. Creanzaa,c, N. De Filippisa,c,1, M. De Palmaa,b, L. Fiorea, G. Iasellia,c, L. Lusitoa,b, G. Maggia,c, M. Maggia, N. Mannaa,b, B. Marangellia,b, S. Mya,c, S. Nuzzoa,b, N. Pacificoa,b, A. Pompilia,b, G. Pugliesea,c, F. Romanoa,c, G. Selvaggia,b, L. Silvestrisa, G. Singha,b, S. Tupputia,b, G. Zitoa
INFN Sezione di Bolognaa, Universit`a di Bolognab, Bologna, Italy
G. Abbiendia, G. Barozzi, A.C. Benvenutia, D. Bonacorsia,b, S. Braibant-Giacomellia,b, L. Brigliadoria,b, P. Capiluppia,b, A. Castroa,b, F.R. Cavalloa, M. Cuffiania,b, G.M. Dallavallea, F. Fabbria, A. Fanfania,b, D. Fasanellaa,b,1, P. Giacomellia, C. Grandia, S. Marcellinia, G. Masettia, M. Meneghellia,b, A. Montanaria, F.L. Navarriaa,b, F. Odoricia, A. Perrottaa, F. Primaveraa,b, A.M. Rossia,b, T. Rovellia,b, G. Sirolia,b, R. Travaglinia,b
INFN Sezione di Cataniaa, Universit`a di Cataniab, Catania, Italy
S. Albergoa,b, G. Cappelloa,b, M. Chiorbolia,b, S. Costaa,b, R. Potenzaa,b, A. Tricomia,b, C. Tuvea,b
INFN Sezione di Firenzea, Universit`a di Firenzeb, Firenze, Italy
G. Barbaglia, V. Ciullia,b, C. Civininia, R. D’Alessandroa,b, E. Focardia,b, S. Frosalia,b, E. Galloa, S. Gonzia,b, M. Meschinia, S. Paolettia, G. Sguazzonia, A. Tropianoa,1
INFN Laboratori Nazionali di Frascati, Frascati, Italy
L. Benussi, S. Bianco, S. Colafranceschi24, F. Fabbri, D. Piccolo
INFN Sezione di Genova, Genova, Italy
P. Fabbricatore, R. Musenich
INFN Sezione di Milano-Bicoccaa, Universit`a di Milano-Bicoccab, Milano, Italy
A. Benagliaa,b,1, F. De Guioa,b, L. Di Matteoa,b, S. Fiorendia,b, S. Gennaia,1, A. Ghezzia,b, S. Malvezzia, R.A. Manzonia,b, A. Martellia,b, A. Massironia,b,1, D. Menascea, L. Moronia, M. Paganonia,b, D. Pedrinia, S. Ragazzia,b, N. Redaellia, S. Salaa, T. Tabarelli de Fatisa,b
INFN Sezione di Napolia, Universit`a di Napoli ”Federico II”b, Napoli, Italy
S. Buontempoa, C.A. Carrillo Montoyaa,1, N. Cavalloa,25, A. De Cosaa,b, O. Doganguna,b, F. Fabozzia,25, A.O.M. Iorioa,1, L. Listaa, M. Merolaa,b, P. Paoluccia
INFN Sezione di Padovaa, Universit`a di Padovab, Universit`a di Trento (Trento)c, Padova,
Italy
P. Azzia, N. Bacchettaa,1, P. Bellana,b, D. Biselloa,b, A. Brancaa, R. Carlina,b, P. Checchiaa, T. Dorigoa, U. Dossellia, F. Fanzagoa, F. Gasparinia,b, U. Gasparinia,b, A. Gozzelinoa, K. Kanishchev, S. Lacapraraa,26, I. Lazzizzeraa,c, M. Loretia, M. Margonia,b, M. Mazzucatoa, A.T. Meneguzzoa,b, M. Nespoloa,1, L. Perrozzia, N. Pozzobona,b, P. Ronchesea,b, F. Simonettoa,b, E. Torassaa, M. Tosia,b,1, S. Vaninia,b, P. Zottoa,b, G. Zumerlea,b
INFN Sezione di Paviaa, Universit`a di Paviab, Pavia, Italy
U. Berzanoa, M. Gabusia,b, S.P. Rattia,b, C. Riccardia,b, P. Torrea,b, P. Vituloa,b
INFN Sezione di Perugiaa, Universit`a di Perugiab, Perugia, Italy
M. Biasinia,b, G.M. Bileia, B. Caponeria,b, L. Fan `oa,b, P. Laricciaa,b, A. Lucaronia,b,1, G. Mantovania,b, M. Menichellia, A. Nappia,b, F. Romeoa,b, A. Santocchiaa,b, S. Taronia,b,1, M. Valdataa,b
INFN Sezione di Pisaa, Universit`a di Pisab, Scuola Normale Superiore di Pisac, Pisa, Italy
P. Azzurria,c, G. Bagliesia, T. Boccalia, G. Broccoloa,c, R. Castaldia, R.T. D’Agnoloa,c, R. Dell’Orsoa, F. Fioria,b, L. Fo`aa,c, A. Giassia, A. Kraana, F. Ligabuea,c, T. Lomtadzea, L. Martinia,27, A. Messineoa,b, F. Pallaa, F. Palmonaria, A. Rizzi, A.T. Serbana, P. Spagnoloa, R. Tenchinia, G. Tonellia,b,1, A. Venturia,1, P.G. Verdinia
INFN Sezione di Romaa, Universit`a di Roma ”La Sapienza”b, Roma, Italy
L. Baronea,b, F. Cavallaria, D. Del Rea,b,1, M. Diemoza, C. Fanelli, M. Grassia,1, E. Longoa,b, P. Meridiania, F. Micheli, S. Nourbakhsha, G. Organtinia,b, F. Pandolfia,b, R. Paramattia, S. Rahatloua,b, M. Sigamania, L. Soffi
INFN Sezione di Torino a, Universit`a di Torino b, Universit`a del Piemonte Orientale
(No-vara)c, Torino, Italy
N. Amapanea,b, R. Arcidiaconoa,c, S. Argiroa,b, M. Arneodoa,c, C. Biinoa, C. Bottaa,b, N. Cartigliaa, R. Castelloa,b, M. Costaa,b, N. Demariaa, A. Grazianoa,b, C. Mariottia,1, S. Masellia, E. Migliorea,b, V. Monacoa,b, M. Musicha, M.M. Obertinoa,c, N. Pastronea, M. Pelliccionia, A. Potenzaa,b, A. Romeroa,b, M. Ruspaa,c, R. Sacchia,b, V. Solaa,b, A. Solanoa,b, A. Staianoa, A. Vilela Pereiraa
INFN Sezione di Triestea, Universit`a di Triesteb, Trieste, Italy
S. Belfortea, F. Cossuttia, G. Della Riccaa,b, B. Gobboa, M. Maronea,b, D. Montaninoa,b,1, A. Penzoa
Kangwon National University, Chunchon, Korea
S.G. Heo, S.K. Nam
Kyungpook National University, Daegu, Korea
S. Chang, J. Chung, D.H. Kim, G.N. Kim, J.E. Kim, D.J. Kong, H. Park, S.R. Ro, D.C. Son
Chonnam National University, Institute for Universe and Elementary Particles, Kwangju, Korea
J.Y. Kim, Zero J. Kim, S. Song
Konkuk University, Seoul, Korea
H.Y. Jo
Korea University, Seoul, Korea
S. Choi, D. Gyun, B. Hong, M. Jo, H. Kim, T.J. Kim, K.S. Lee, D.H. Moon, S.K. Park, E. Seo, K.S. Sim
University of Seoul, Seoul, Korea
M. Choi, S. Kang, H. Kim, J.H. Kim, C. Park, I.C. Park, S. Park, G. Ryu
Sungkyunkwan University, Suwon, Korea
Y. Cho, Y. Choi, Y.K. Choi, J. Goh, M.S. Kim, B. Lee, J. Lee, S. Lee, H. Seo, I. Yu
Vilnius University, Vilnius, Lithuania
M.J. Bilinskas, I. Grigelionis, M. Janulis
Centro de Investigacion y de Estudios Avanzados del IPN, Mexico City, Mexico
H. Castilla-Valdez, E. De La Cruz-Burelo, I. Heredia-de La Cruz, R. Lopez-Fernandez, R. Maga ˜na Villalba, J. Mart´ınez-Ortega, A. S´anchez-Hern´andez, L.M. Villasenor-Cendejas
Universidad Iberoamericana, Mexico City, Mexico
Benemerita Universidad Autonoma de Puebla, Puebla, Mexico
H.A. Salazar Ibarguen
Universidad Aut ´onoma de San Luis Potos´ı, San Luis Potos´ı, Mexico
E. Casimiro Linares, A. Morelos Pineda, M.A. Reyes-Santos
University of Auckland, Auckland, New Zealand
D. Krofcheck
University of Canterbury, Christchurch, New Zealand
A.J. Bell, P.H. Butler, R. Doesburg, S. Reucroft, H. Silverwood
National Centre for Physics, Quaid-I-Azam University, Islamabad, Pakistan
M. Ahmad, M.I. Asghar, H.R. Hoorani, S. Khalid, W.A. Khan, T. Khurshid, S. Qazi, M.A. Shah, M. Shoaib
Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Warsaw, Poland
G. Brona, M. Cwiok, W. Dominik, K. Doroba, A. Kalinowski, M. Konecki, J. Krolikowski
Soltan Institute for Nuclear Studies, Warsaw, Poland
H. Bialkowska, B. Boimska, T. Frueboes, R. Gokieli, M. G ´orski, M. Kazana, K. Nawrocki, K. Romanowska-Rybinska, M. Szleper, G. Wrochna, P. Zalewski
Laborat ´orio de Instrumenta¸c˜ao e F´ısica Experimental de Part´ıculas, Lisboa, Portugal
N. Almeida, P. Bargassa, A. David, P. Faccioli, P.G. Ferreira Parracho, M. Gallinaro, P. Musella, A. Nayak, J. Pela1, P.Q. Ribeiro, J. Seixas, J. Varela, P. Vischia
Joint Institute for Nuclear Research, Dubna, Russia
I. Belotelov, I. Golutvin, N. Gorbounov, I. Gramenitski, A. Kamenev, V. Karjavin, V. Konoplyanikov, V. Korenkov, G. Kozlov, A. Lanev, P. Moisenz, V. Palichik, V. Perelygin, M. Savina, S. Shmatov, S. Vasil’ev, A. Zarubin
Petersburg Nuclear Physics Institute, Gatchina (St Petersburg), Russia
S. Evstyukhin, V. Golovtsov, Y. Ivanov, V. Kim, P. Levchenko, V. Murzin, V. Oreshkin, I. Smirnov, V. Sulimov, L. Uvarov, S. Vavilov, A. Vorobyev, An. Vorobyev
Institute for Nuclear Research, Moscow, Russia
Yu. Andreev, A. Dermenev, S. Gninenko, N. Golubev, M. Kirsanov, N. Krasnikov, V. Matveev, A. Pashenkov, A. Toropin, S. Troitsky
Institute for Theoretical and Experimental Physics, Moscow, Russia
V. Epshteyn, M. Erofeeva, V. Gavrilov, M. Kossov1, A. Krokhotin, N. Lychkovskaya, V. Popov, G. Safronov, S. Semenov, V. Stolin, E. Vlasov, A. Zhokin
Moscow State University, Moscow, Russia
A. Belyaev, E. Boos, M. Dubinin4, L. Dudko, A. Ershov, A. Gribushin, O. Kodolova, I. Lokhtin, A. Markina, S. Obraztsov, M. Perfilov, S. Petrushanko, L. Sarycheva†, V. Savrin, A. Snigirev
P.N. Lebedev Physical Institute, Moscow, Russia
V. Andreev, M. Azarkin, I. Dremin, M. Kirakosyan, A. Leonidov, G. Mesyats, S.V. Rusakov, A. Vinogradov
State Research Center of Russian Federation, Institute for High Energy Physics, Protvino, Russia
V. Krychkine, V. Petrov, R. Ryutin, A. Sobol, L. Tourtchanovitch, S. Troshin, N. Tyurin, A. Uzunian, A. Volkov
University of Belgrade, Faculty of Physics and Vinca Institute of Nuclear Sciences, Belgrade, Serbia
P. Adzic28, M. Djordjevic, M. Ekmedzic, D. Krpic28, J. Milosevic
Centro de Investigaciones Energ´eticas Medioambientales y Tecnol ´ogicas (CIEMAT), Madrid, Spain
M. Aguilar-Benitez, J. Alcaraz Maestre, P. Arce, C. Battilana, E. Calvo, M. Cerrada, M. Chamizo Llatas, N. Colino, B. De La Cruz, A. Delgado Peris, C. Diez Pardos, D. Dom´ınguez V´azquez, C. Fernandez Bedoya, J.P. Fern´andez Ramos, A. Ferrando, J. Flix, M.C. Fouz, P. Garcia-Abia, O. Gonzalez Lopez, S. Goy Lopez, J.M. Hernandez, M.I. Josa, G. Merino, J. Puerta Pelayo, I. Redondo, L. Romero, J. Santaolalla, M.S. Soares, C. Willmott
Universidad Aut ´onoma de Madrid, Madrid, Spain
C. Albajar, G. Codispoti, J.F. de Troc ´oniz
Universidad de Oviedo, Oviedo, Spain
J. Cuevas, J. Fernandez Menendez, S. Folgueras, I. Gonzalez Caballero, L. Lloret Iglesias, J. Piedra Gomez29, J.M. Vizan Garcia
Instituto de F´ısica de Cantabria (IFCA), CSIC-Universidad de Cantabria, Santander, Spain
J.A. Brochero Cifuentes, I.J. Cabrillo, A. Calderon, S.H. Chuang, J. Duarte Campderros, M. Felcini30, M. Fernandez, G. Gomez, J. Gonzalez Sanchez, C. Jorda, P. Lobelle Pardo, A. Lopez Virto, J. Marco, R. Marco, C. Martinez Rivero, F. Matorras, F.J. Munoz Sanchez, T. Rodrigo, A.Y. Rodr´ıguez-Marrero, A. Ruiz-Jimeno, L. Scodellaro, M. Sobron Sanudo, I. Vila, R. Vilar Cortabitarte
CERN, European Organization for Nuclear Research, Geneva, Switzerland
D. Abbaneo, E. Auffray, G. Auzinger, P. Baillon, A.H. Ball, D. Barney, C. Bernet5, W. Bialas, G. Bianchi, P. Bloch, A. Bocci, H. Breuker, K. Bunkowski, T. Camporesi, G. Cerminara, T. Christiansen, J.A. Coarasa Perez, B. Cur´e, D. D’Enterria, A. De Roeck, S. Di Guida, M. Dobson, N. Dupont-Sagorin, A. Elliott-Peisert, B. Frisch, W. Funk, A. Gaddi, G. Georgiou, H. Gerwig, M. Giffels, D. Gigi, K. Gill, D. Giordano, M. Giunta, F. Glege, R. Gomez-Reino Garrido, P. Govoni, S. Gowdy, R. Guida, L. Guiducci, M. Hansen, P. Harris, C. Hartl, J. Harvey, B. Hegner, A. Hinzmann, H.F. Hoffmann, V. Innocente, P. Janot, K. Kaadze, E. Karavakis, K. Kousouris, P. Lecoq, P. Lenzi, C. Lourenc¸o, T. M¨aki, M. Malberti, L. Malgeri, M. Mannelli, L. Masetti, G. Mavromanolakis, F. Meijers, S. Mersi, E. Meschi, R. Moser, M.U. Mozer, M. Mulders, E. Nesvold, M. Nguyen, T. Orimoto, L. Orsini, E. Palencia Cortezon, E. Perez, A. Petrilli, A. Pfeiffer, M. Pierini, M. Pimi¨a, D. Piparo, G. Polese, L. Quertenmont, A. Racz, W. Reece, J. Rodrigues Antunes, G. Rolandi31, T. Rommerskirchen, C. Rovelli32, M. Rovere, H. Sakulin, F. Santanastasio, C. Sch¨afer, C. Schwick, I. Segoni, A. Sharma, P. Siegrist, P. Silva, M. Simon, P. Sphicas33, D. Spiga, M. Spiropulu4, M. Stoye, A. Tsirou, G.I. Veres16, P. Vichoudis, H.K. W ¨ohri, S.D. Worm34, W.D. Zeuner
Paul Scherrer Institut, Villigen, Switzerland
W. Bertl, K. Deiters, W. Erdmann, K. Gabathuler, R. Horisberger, Q. Ingram, H.C. Kaestli, S. K ¨onig, D. Kotlinski, U. Langenegger, F. Meier, D. Renker, T. Rohe, J. Sibille35
Institute for Particle Physics, ETH Zurich, Zurich, Switzerland
L. B¨ani, P. Bortignon, M.A. Buchmann, B. Casal, N. Chanon, Z. Chen, A. Deisher, G. Dissertori, M. Dittmar, M. D ¨unser, J. Eugster, K. Freudenreich, C. Grab, P. Lecomte, W. Lustermann,
P. Martinez Ruiz del Arbol, N. Mohr, F. Moortgat, C. N¨ageli36, P. Nef, F. Nessi-Tedaldi, L. Pape, F. Pauss, M. Peruzzi, F.J. Ronga, M. Rossini, L. Sala, A.K. Sanchez, M.-C. Sawley, A. Starodumov37, B. Stieger, M. Takahashi, L. Tauscher†, A. Thea, K. Theofilatos, D. Treille, C. Urscheler, R. Wallny, H.A. Weber, L. Wehrli, J. Weng
Universit¨at Z ¨urich, Zurich, Switzerland
E. Aguilo, C. Amsler, V. Chiochia, S. De Visscher, C. Favaro, M. Ivova Rikova, B. Millan Mejias, P. Otiougova, P. Robmann, H. Snoek, M. Verzetti
National Central University, Chung-Li, Taiwan
Y.H. Chang, K.H. Chen, C.M. Kuo, S.W. Li, W. Lin, Z.K. Liu, Y.J. Lu, D. Mekterovic, R. Volpe, S.S. Yu
National Taiwan University (NTU), Taipei, Taiwan
P. Bartalini, P. Chang, Y.H. Chang, Y.W. Chang, Y. Chao, K.F. Chen, C. Dietz, U. Grundler, W.-S. Hou, Y. Hsiung, K.Y. Kao, Y.J. Lei, R.-W.-S. Lu, D. Majumder, E. Petrakou, X. Shi, J.G. Shiu, Y.M. Tzeng, M. Wang
Cukurova University, Adana, Turkey
A. Adiguzel, M.N. Bakirci38, S. Cerci39, C. Dozen, I. Dumanoglu, E. Eskut, S. Girgis, G. Gokbulut, I. Hos, E.E. Kangal, G. Karapinar, A. Kayis Topaksu, G. Onengut, K. Ozdemir, S. Ozturk40, A. Polatoz, K. Sogut41, D. Sunar Cerci39, B. Tali39, H. Topakli38, D. Uzun, L.N. Vergili, M. Vergili
Middle East Technical University, Physics Department, Ankara, Turkey
I.V. Akin, T. Aliev, B. Bilin, S. Bilmis, M. Deniz, H. Gamsizkan, A.M. Guler, K. Ocalan, A. Ozpineci, M. Serin, R. Sever, U.E. Surat, M. Yalvac, E. Yildirim, M. Zeyrek
Bogazici University, Istanbul, Turkey
M. Deliomeroglu, E. G ¨ulmez, B. Isildak, M. Kaya42, O. Kaya42, S. Ozkorucuklu43, N. Sonmez44
National Scientific Center, Kharkov Institute of Physics and Technology, Kharkov, Ukraine
L. Levchuk
University of Bristol, Bristol, United Kingdom
F. Bostock, J.J. Brooke, E. Clement, D. Cussans, H. Flacher, R. Frazier, J. Goldstein, M. Grimes, G.P. Heath, H.F. Heath, L. Kreczko, S. Metson, D.M. Newbold34, K. Nirunpong, A. Poll, S. Senkin, V.J. Smith, T. Williams
Rutherford Appleton Laboratory, Didcot, United Kingdom
L. Basso45, K.W. Bell, A. Belyaev45, C. Brew, R.M. Brown, D.J.A. Cockerill, J.A. Coughlan, K. Harder, S. Harper, J. Jackson, B.W. Kennedy, E. Olaiya, D. Petyt, B.C. Radburn-Smith, C.H. Shepherd-Themistocleous, I.R. Tomalin, W.J. Womersley
Imperial College, London, United Kingdom
R. Bainbridge, G. Ball, R. Beuselinck, O. Buchmuller, D. Colling, N. Cripps, M. Cutajar, P. Dauncey, G. Davies, M. Della Negra, W. Ferguson, J. Fulcher, D. Futyan, A. Gilbert, A. Guneratne Bryer, G. Hall, Z. Hatherell, J. Hays, G. Iles, M. Jarvis, G. Karapostoli, L. Lyons, A.-M. Magnan, J. Marrouche, B. Mathias, R. Nandi, J. Nash, A. Nikitenko37, A. Papageorgiou, M. Pesaresi, K. Petridis, M. Pioppi46, D.M. Raymond, S. Rogerson, N. Rompotis, A. Rose, M.J. Ryan, C. Seez, A. Sparrow, A. Tapper, S. Tourneur, M. Vazquez Acosta, T. Virdee, S. Wakefield, N. Wardle, D. Wardrope, T. Whyntie
